Stent delivery systems for expandable stents typically employ a push-pull mechanism to introduce the stent into the body. For example, stent delivery systems generally include an outer sheath coaxially disposed and slidable over an inner catheter. The stent is disposed at the distal end of the delivery system in between the inner catheter and the outer sheath. The inner catheter and the outer sheath move coaxially with respect to each other to expose the stent at a delivery position. A self-expanding stent may be deployed at the delivery site by proximally pulling back the outer sheath relative to the inner catheter until the stent is exposed and expands away from the inner catheter. An outer sheath may also be used with balloon expandable or other types of expandable stents, for example to protect the stent during delivery to the patient. Some of the stent delivery systems also include a flushing port.
There are numerous drawbacks to the above push-pull delivery device. For example, utilizing a conventional push-pull delivery device may cause the physician to inadvertently use excessive force and pull back the outer sheath too far, thereby prematurely deploying the stent in an incorrect position within a body lumen. At this step in the procedure, repositioning of the stent becomes difficult, if not impossible, because the stent has already radially self-expanded into the body lumen. Additionally, controlled retraction of the outer sheath may not be achieved when the physician is manually retracting the outer catheter. Manual retraction of the outer sheath may lead to inadvertent jerking back of the outer sheath and difficulty in proper placement of the stent. Furthermore, two hands are typically needed to deploy the prosthesis with a push-pull mechanism. One hand may be required to hold the inner catheter while the other hand pulls the outer sheath and slides it back over the inner catheter. The use of two hands prevents the physician from performing another task during the procedure.
In view of the drawbacks of the typical push-pull delivery system, a delivery system that can increase the control, accuracy and ease of placement during deployment of a stent has been developed as described in U.S. Patent Publication 2009/0024133. In some situations, it is advantageous to include a flushing system with a stent delivery system to flush air or other particles from the delivery system prior to use. What is needed is a flushing system that can be used with a controlled stent delivery system that allows the physician to flush the stent within a flushable stent chamber without interfering with the delivery system control for moving the outer sheath relative to the inner catheter. Although the flushing system described below may be useful with the delivery system for increasing the control, accuracy and ease of placement during deployment of the stent, the flushing system may also solve other problems.